MONDAY Sept. 16, 2013 -- Children of same-sex parents are less likely than their peers to have private health insurance, but the disparity shrinks in states that recognize legal same-sex unions, a new U.S. study finds.

The results are not surprising, experts say, because employers have not had to extend health benefits to an employee's same-sex partner -- or that partner's children.

But the study does highlight a less-talked-about aspect of the debate on gay marriage, said lead researcher Gilbert Gonzales, a Ph.D. candidate in health policy and management at the University of Minnesota in Minneapolis.

"We're fairly certain from past research that access to health insurance does directly affect children's health," Gonzales said. But there's been little research into whether same-sex couples' kids lack access.

Using data from a large federal survey, the investigators found that about two-thirds of U.S. children and teens with same-sex parents had private health insurance (63 percent of those with two fathers, and about 68 percent with two mothers).

That compared with about 78 percent of kids with married heterosexual parents, the researchers report online Sept. 16 in Pediatrics.

And when they weighed other factors -- such as parents' incomes and education -- the researchers found that kids living with same-sex parents were 39 percent to 45 percent less likely to have private health insurance versus those with a married mom and dad.

The results looked different, however, in states that allowed gay marriage or civil unions, or had comprehensive domestic partnership laws, Gonzales said.

In those states, kids living with two mothers were no less likely to have private insurance, though their peers with two fathers still were. And there were no clear disparities in states that allowed "second-parent adoptions" -- which means both partners in a same-sex relationship can be their child's legally adoptive parent.

"I think we are going to see more and more research like this that shows how marriage-equality laws have far-reaching health consequences," said Richard Wight, a researcher at the University of California, Los Angeles, whose work has found a link between legal unions and better mental health for gay and lesbian adults.

Wight likened marriage equality to a "structural intervention." That refers to any broad policy, from seatbelt laws to fluoride in drinking water, that can affect people's well-being -- "sometimes without them even realizing it," Wight noted.

"Increasingly," he said, "research is demonstrating that laws legalizing same-sex marriages are advantageous to health."

The current study did not look at children's actual well-being. But like Gonzales, Wight pointed to the known correlation between access to health insurance and children's health.

Right now, 13 U.S. states and the District of Columbia allow gay marriage, and another six recognize civil unions or domestic partnerships that include full spousal and family rights. Eighteen states allow second-parent adoptions.

In June, the U.S. Supreme Court struck down the portion of the Defense of Marriage Act (DOMA) that barred the federal government from recognizing same-sex marriage. The decision opened the door for same-sex couples who are legally married in their state to receive the same federal benefits as heterosexual married couples do.

That may make it easier for some children of same-sex couples to get health insurance, Gonzales said.

As it stood, even couples who were legally married in their state faced barriers to getting employer-sponsored health insurance for their families. Because federal law did not recognize the marriage, health coverage for a spouse or children was considered income -- and it was taxed. So same-sex married employees had to pay more out of their own pockets than their heterosexual counterparts did. Their employers also had bigger costs, in the form of a higher payroll tax.

Without the tax obstacle, same-sex couples may have an easier time, said Gonzales. It's not clear what could happen in states without legal same-sex unions, but Gonzales noted that many large companies have been voluntarily extending health insurance to the families of gay and lesbian employees.

Last month, for example, Wal-Mart -- the nation's largest private employer -- said it would start offering health benefits to U.S. employees' domestic partners, including those of the same sex.

The current findings, which support the American Academy of Pediatrics' endorsements of same-sex marriage, are based on data from a 2008-2010 Census Bureau Survey. It covered 5,081 U.S. children and teens living with same-sex parents, nearly 1.4 million who were living with a married mother and father, and more than 100,000 living with an unmarried mom and dad.

Along with the discrepancy in private health coverage, the researchers found that 10 percent of kids with two fathers were uninsured versus less than 7 percent of those with a married mother and father. Just over 7 percent of kids living with two mothers were uninsured.

Children of same-sex parents were also more often on public insurance -- with about one-quarter getting benefits, compared with 16 percent of kids with married heterosexual parents.

If legal same-sex marriage does boost private health coverage for kids, Wight said it could be a "win-win" for those families and for the public in general.